The field of the invention is an airborne radar employing electronic scanned array with a transmission array and a dual receive arrays employing diplaced center antenna (DPCA) methodology to detect moving targets in and out of clutter and measure there speed and azimuth very accurately
1. Background of the Invention
In the field of this invention clutter has been a major impediment. Clutter being the unwanted signals from stationary ground that mixes with moving targets that makes it very difficult to obtain the objective of this invention.
The background in the state of the art, in airborne radars that detect moving targets in the presence of ground clutter and measuring their range, radial velocity and azimuth, consists of the following:
1. Delay line cancellor Systems
2. Monopulse Systems
3. Two subarray DPCA radar
4. Three Subarray DPCA Radar
1. The Delay Line cancellor subtracts the inputs from the radar of two consecutive pulses. If the moving target is in the presence of Main Beam clutter it looks just like clutter and cannot be detected and therefore cannot measure its parameters. The E2C Hawkeye-Grumman is an example of this system where a double delay line cancellor plus special filtering is implemented.
2. Monopulse System Utilizing delay line cancellor at the input because of the system cannot determine the radial velocity and azimuth in the presence of clutter. It utilizes two subarrays, a sum (xcex94xcexa3) array and a difference (xcex94) array to process the data. The accuracy is limited by the ratio of the noise of the difference channel and ten to one ratio is about the limit. It has better accuracy than delay line cancellor but more processing and its notable to detect and process moving targets. Like the delay line cancellor it can not detect targets in main lobe clutter.
3. The DPCA Radar with two subarrays using system in classical theory a moving targets precise angle and radial velocity can not be determined. The detection of the moving target may be obtained only. This is the reason for three segment antenna to attain the precise velocity and azimuth.
4. The DPCA Radar with three subarrays attains the objective of detecting a moving target in the presence of clutter and measuring its radial velocity and azimuth position but takes three subarrays (large amount of hardware and processing since it has three subarrays it has to process and must perfom many logic and mathematical operations)
Example: Northrop Grumman JSTARS System.
2. Description of Prior Art
Patent Ser. No. 766,309 Filed Aug. 16, 1985xe2x80x94Abandoned
Entitled: Two Port Clutter Suppression Interfermometry System For
Radar Detection of Targets
Inventor: Thomas J. Cataldo
Grumman Reference: 388-GAC; P-1(3783)
This patent has the same objective and the same inventor as the aforementioned invention. This invention is not obvious from the previous patent stated above with one of ordinary skill in the art. This invention has many essentially independent techniques to attain the objective.
The patent above discloses a vague geometric technique which takes advantage of the first order change in target relative to clutter (which was considered changing very slowly).
U.S. Pat. No. 5,563,601 Filed Oct. 18, 1996
Entitled: Two Port Clutter Synthetic Aperture Radar System For
Radar Detection of Targets
Inventor: Thomas J. Cataldo
Northrup-Grumman
The patent above has the same objective and inventor as in contrast to existing dual array radar systems, the present invention employs a different principle. The principle is that it depends on a moving target creating a black hole (lack of signal) behind it, as well as when the target moves it both suppresses clutter at where its moved and exposes clutter(increased signal) from where it hap moved.
The range doppler bins, with this technique have to be relatively small to be an effective technique.
U.S. Pat. No. 4,885,590 Filed Apr. 14, 1989 Issuedxe2x80x94Dec. 5, 1989
Entitled: Blind Speed Elimination For Dual Displaced Phase Center
Antenna Radar Processor Mounted on a Moving Platform
Inventor: Hassan; Moh""d A
General Electric Company (Moorestown, N.J.)
The patent above employs the dual displaced phase center antenna to eliminate blind speeds of targets but not to not to attain precisely there relative radial velocity and azimuth position in the presence of main lobe clutter.
This patent develops the mathematical basis and the physical radar principles and computer simulation results are the basis for the many techniques developed.
This invention considers the whole system from the application and mode of operation for all the essential elements of the system and the many possible implementations. Each part of the system is analyzed and optimized as much as possible to aid any techniques to attain the objective of the invention. The following are essential parts of the system (there are a number of supporting depending implementations for the optimization of the system) as follows:
(a) Antenna Look Angle
(b) Antenna Configuration
(c) RF Frequency
(d) PRF
(e) Apertures
(f) Beamwidth of antenna arrays
(g) Groups of radar data to process
(h) Weighting functions for clutter and target
(i) Error reduction techniques
(j) Antenna match considerations
(k) Adaptive techniques for the cancellation of clutter
(l) Management, control and optimization of implementation
(m) Others
The many techniques developed to attain the objective are unique and based on extensive mathematical development and computer simulation of radar principles and employing real radar data.
This invention is special synthetic aperture radar. It is a dual synthetic aperture radar. It is implemented in a special array (which may be formed by combining the two identical receiving arrays). The motion of the platform carrying the receiving arrays is such that on some number of succeeding radar pulses, the second antenna travels xc2xd distance between two receiving (displaced phase center antenna) the same space as the first antenna array (FIGS. 1 to 3xe2x80x94Basic Concept of DSARS). This is continued until the two synthetic arrays are formed. When the radar data is spectrally processed and subtracted from each other, the clutter in both arrays being identical are cancelled and the target being different is detected (FIGS. 1 and 2). The target parameters are such as the relative radial velocity and angular position are not yet determined. There is not enough processing at this point.
The object of this invention is to further process the radar data from two synthetic arrays and determine very accurately the range, relative radial velocity and angular position of the target (within the resolution of a doppler bin or better). The target may be in the presence of clutter or out of clutter. The essential contribution of this radar system is to be more cost effective than the more hardware system such as those using three or more receive arrays and much more capable and accurate than the delay line or monopulse systems